4XX

400 Bad Request                # malformed request syntax, size too large

401 Unauthorized               # for use when authentication is required

403 Forbidden

404 Not Found

405 Method Not Allowed

408 Request Timeout

410 Gone

413 Payload Too Large

414 URI Too Long

426 Upgrade Required

429 Too Many Requests

431 Request Header Fields Too Large

5XX

503 Service Unavailable

The server is currently unable to handle the request due to a temporary overload or scheduled maintenance,

which will likely be alleviated after some delay.